Technical Field
The present invention relates to a technique for displaying a result, of an area extraction on an image, in an easily recognizable manner.
Related Art
Processing called area extraction (segmentation) is one type of digital image processing performed by a computer. The area extraction processing is processing of dividing a target image into a foreground (portion to be extracted) and a background (other portions), based on image features such as colors and edge. The processing is used for a purpose of extracting a portion of an object or a person as a target of image processing or image recognition, for example.
Various algorithms for the area extraction processing have been proposed, and the extraction accuracy of the area extraction processing has improved. However, there is no guarantee that only a portion, intended by a user, is extracted without fail by performing the processing only once. Therefore, most systems have a function of displaying an extraction result on a screen, so as to allow the user to check the sufficiency of the foreground area or whether the processing needs to be started over. Methods for displaying the extraction result include: a method of drawing a contour line of the extracted foreground area on an original image (see Non Patent Literature 1); a method of covering a background area with a mask image so that only the foreground area is displayed (see Non Patent Literature 2); a method of overlaying a mask image of a single color, representing the foreground area or the background area, on the original image to be displayed (see Non Patent Literature 3); and the like.
In conventional systems, the contour line and the mask image are drawn with an eye-catching color such as magenta and yellow in many cases, to achieve high visibility of the contour line and the mask image representing the extraction result. However, when the foreground or the background of the original image includes a color similar to the color with which the contour line or the mask image is drawn, the range of the contour line and the mask image becomes unclear. Thus, whether an area is sufficiently extracted is difficult to be determined, if not impossible. Conventionally, to deal with such a situation, the user has switched between displaying and non-displaying of the contour line or the mask image, to distinguish between the color of the contour line or the mask image with the color of the original image. In a system where the drawn color can be changed, the user himself or herself has selected a color with high visibility. However, such conventional methods impose an extra operation load on the user. Furthermore, when the original image includes various hues, an appropriate drawing color might be difficult to determine.